Urban Forest Tempers Heat Waves – San Diego Downtown News


San Diego is expected to be hit by another record-breaking heat wave over Labor Day weekend. As shocking as skyrocketing temperatures are, they are becoming routine in Southern California where the effects of climate change continue to worsen.

Amid efforts to stay cool and fight climate change, the city has a secret weapon: its urban forest. On an individual level, it’s easy to walk under a shaded area and feel how much cooler it is than being in direct sunlight. Extended to the community level, a neighborhood with large, shady trees can be up to 20 degrees cooler than a neighborhood without mature trees populating the landscape.

“Trees are known to cool neighborhoods in the summer by reducing the heat island effect through shading and evapotranspiration where trees absorb moisture through the ground and release it. [it] in the air through the leaves of the tree,” said Brian Widener, City of San Diego Forester.

Many aspects of the built environment can make high temperatures worse. Pavement, cement and the facades of large buildings can all be absorbent surfaces that heat up faster and trap heat longer than the natural environment. This heat island effect means that urban areas can experience higher temperatures than outlying rural areas.

Although the ocean breeze mitigates this in coastal parts of San Diego, another way to prevent this effect is to use trees.

“Trees provide shade, support biodiversity and help fight climate change by absorbing carbon dioxide. Equally important, trees, with their lush canopy, help reduce the heat island effect,” said Jimmie Webb, SDG&E Utility Forester.

The urban forest is an important aspect of San Diego’s climate action plan since trees capture and store carbon. In the updated CAP, San Diego plans to plant 40,000 new trees by 2030 and 100,000 by 2035 – the deadline for the city to reach zero greenhouse gas emissions. According to Widener, every effort is made to nurture the trees already growing in city streets and parks. Large trees store more carbon than young trees, so their loss is particularly important.

“As we increase the CO2 in our atmosphere which contributes to rising temperatures, trees are a great way to pull that carbon out of the atmosphere over the long term. [storage] in branches and trunks,” said Vince Mikulanis, Western Operations Manager for the Davey Resource Group.

SDG&E has made a similar commitment to plant 10,000 trees per year in its service area. At least 2,500 of these trees will be inside the city limits over the next decade. One of the reasons SDG&E made this commitment was the need to occasionally cut down trees that disrupt power lines. Although tree removal is the last scenario after other options, such as pruning or reshaping trees to grow around power lines, have failed, the utility has found that not all customers did not want the company to replace the trees on their property. They have taken this task on themselves and help empower customers who want to plant trees through the Community Tree Rebate program and free consultations with arborists.

The city has a similar program, Free Tree SD, where residents can request that a street tree be planted near them as long as they commit to watering the tree for three years.

Despite the best efforts of arborists to keep trees alive, there are times when a tree is dead or needs to be removed. Traditionally, a dead tree in the city was cut down into firewood, sent to a landfill, or ground into woodchips. All of these methods mean that the carbon stored in the branches and trunk of the tree throughout its life will be released into the atmosphere when the wood is exposed to oxygen.

This carbon cycle is carbon neutral and a natural process. It would be nice without the massive amounts of greenhouse gases that humans were already releasing into the atmosphere.

“In a world where we’re taking so much more from the earth than we’re giving back, we need ways to slow that decay, to slow the re-emission of greenhouse gas emissions back into the atmosphere,” Tom said. Hamilton, the founder of Lumbercycle.

Lumbercycle is one of the few local organizations diverting these trees from landfills and using them as urban lumber. The ultimate goal is to have a sustainable urban forest. When a dead tree is turned into wood which is then dried and made into furniture, the wood decomposes much more slowly. The tree’s carbon is sequestered inside this furniture rather than being released into the atmosphere.

The urban forest has countless other economic and environmental benefits. Trees help manage stormwater drainage and filter pollutants from the air. Dust and debris are caught by the leaves so the air is cleaner. Studies have shown that people will shop longer if there are shady trees outside a store and trees increase property value. Trees also improve the walkability and mobility of cities. Even pavement lasts longer when shaded, requiring less maintenance.

“Trees sort of filter the air we breathe. And that’s why planting in areas like Barrio Logan, where we have shipyards and that kind of activity, [is important] for the citizens who live in those areas,” said Mikulanis, who also serves on the San Diego Urban Forest Regional Council.

With the benefits of the urban forest becoming clearer, many entities have embraced tree planting efforts. San Diego County passed several initiatives on Wednesday, August 31 as part of the regional decarbonization framework, including the expansion of a tree planting program.

“We are continuing progress on a new regional decarbonization roadmap. Today, we took action to accelerate those efforts, including creating an equity-focused tree planting program to reduce heat in urban areas,” said Board of Supervisors Chairman Nathan Fletcher. . “These are important steps to eliminate carbon emissions and protect our environment; and taking these steps will make our region a better place to live for the next generation.

Turning trees into lumber is a complex process that many arborists are unaware of. Lumbercycle helps bridge the gap between arborists and local sawmills. (Photo courtesy Lumbercycle)

Arborists and urban forest managers strive to ensure that the right trees are planted for the future.

Some trees that have resided here for centuries are no longer compatible with the region’s hot weather and dry conditions or will not be in the future as these problems worsen. For example, the city felled an entire grove of redwoods near Balboa Park a few years ago. The native trees were over a hundred years old but could not survive the current conditions.

Another tree that foresters steer clear of is the fan palm. Although palm trees are part of Southern California pop culture mythology, they require frequent maintenance to keep them from being a fire hazard and don’t provide much shade.

SDG&E’s tree planting programs focus on planting shade and fruit trees that will not interfere with above and below ground power lines.

“Part of my job is to educate the public about the need to plant the right tree in the right place to avoid conflicts with utility infrastructure. As a result, our vegetation management team monitors and cares for approximately half a million trees near our infrastructure,” Webb said.

Lumbercycle advocates that amidst tree planting efforts, thought be given to the entire life cycle of the tree, including the wood it might become. One native species that Hamilton hopes to see planted more is black wattle, the wood of which replaces walnut since the popular tree does not grow locally.

For Lumbercycle, the San Diego eucalyptus trees are a huge challenge. As the trees grow in a spiral, it is difficult to dry the wood evenly and it often cracks. Although the supply of dead eucalyptus exceeds Lumbercycle’s ability to use it, the organization has found creative uses for it. As the wood is very hard, the association transformed it into planters in community gardens. The density of the wood means it will rot much slower than other woods, such as pine. They have also used it for hundreds of single benches.

“We can plate eucalyptus logs on a few log bases and because we’ve found that if you’re just going to stick your butt on it, it doesn’t matter if it warps a little bit or cracks a little bit,” Hamilton explained. “It could still be a very nice seat.”

The City of San Diego considers eucalyptus trees an important part of the urban forest.

“Eucalypts are among our largest tree species in the region and contribute significantly to the city’s climate action plan goals for canopy cover and the many other benefits that tall trees provide to our people. communities,” said City Forester Widener. “Taller trees provide more benefits to our communities.”

In addition to which trees to plant, the focus is also on where to plant. Mikulanis noted the need for trees in industrial areas where pollution harms citizens. Meanwhile, the city’s tree-planting efforts through 2030 will largely focus on “communities of concern” that have low opportunity rates according to the Climate Equity Index.

Utility workers help plant trees along a city street. (Photo courtesy of SDG&E)

As part of the Fair Tree Scatter effort, the city has partnered with SDG&E to plant 400 trees in City Heights. Ultimately, these trees will help refresh and improve the walkability of the diverse but impoverished neighborhood.

The partnership between the city, utilities, and nonprofits will help the urban forest mitigate climate change, keep neighborhoods cool, and provide useful wood for the future.